An image forming machine equipped with a transfer belt unit includes a safety detecting means for detecting the completion of setting of an opening/closing member constituting the image forming machine, and a controlling means for controlling the operation of a driving means for a driving roller on the basis of a signal from the safety detecting means. When the safety detecting means signals the completion of the setting after signaling the incompletion of the setting, the controlling means controls the driving means so as to perform a reverse driving, thereby driving the driving roller reversely by a predetermined amount.
